1. Field of the Invention
The present invention relates to a technique for measuring a period of a pulse signal input from outside, for an automotive control device.
2. Description of Related Art Japanese Laid-Open Patent Application Publication No. 2008-309067 discloses that a control device for an internal combustion engine which receives a pulse signal that periodically changes according to an angle of a cam shaft of the internal combustion engine has a filter for removing noise components of the pulse signal.
The use of a digital filter as the filter for removing the noise components of the pulse signal enables a high-precision removal of the noise components. The digital filter, however, periodically operates, which causes a shift between a rising or trailing edge timing of the input pulse signal and an operation timing of the digital filter. This might cause an error between a period of the input pulse signal and a period of the output of the digital filter, and thus might reduce the measurement accuracy of the period.